All arguments must be specified
Usage: /usr/bin/dropbearconvert <inputtype> <outputtype> <inputfile> <outputfile>

CAUTION: This program is for convenience only, and is not secure if used on
untrusted input files, ie it could allow arbitrary code execution.
All parameters must be specified in order.

The input and output types are one of:
openssh
dropbear

Example:
dropbearconvert openssh dropbear /etc/ssh/ssh_host_rsa_key /etc/dropbear_rsa_host_key